1. Field of the Invention
The present invention relates to optical elements such as a lens, a mirror, a prism, a filter and a diffractive optical element, for use in optical equipment such as camera machines including a digital camera, a camera-equipped mobile telephone and the like, projection machines including a video camera, a liquid crystal projector, a liquid crystal rear projector and the like, a telescope, and a microscope, optical information equipment such as an optical pickup, and optical communication equipment such as an optical transceiver module and an optical switch, and also relates to a method of manufacturing the same.
2. Description of the Related Art
In general, an optical system in optical equipment such as a camera machine is configured by a combination of optical elements including a large number of lenses, mirrors, prisms, filters and diffractive optical elements. Further, the optical system is combined with components including a light-emitting device such as an LED, an image display device such as an LCD, a photodetector such as a photodiode or a CCD; thus, an optical equipment is configured. It is essential for assembling the optical system or the optical equipment to correctly align those components with an optical axis. If the optical system or the optical equipment is dislocated from the optical axis, there arises a problem of skew and blurring of an image, so that good image forming performance cannot be obtained.
Conventionally, the optical system has been fabricated by assembling the finely sized optical components including lenses in a frame. As disclosed in JP-A 2003-172807, a technique is known where a lens barrel includes two groups of lenses secured in a frame. It is common in the prior art that the lenses are mounted to a frame for aligning with the optical axis at a practically acceptable degree of precision.
As digital cameras have been marketed widely, some types of them are built in mobile telephones. It is thus desired for reducing of the overall dimensions that the lenses in the optical system are as small as 3 mm in diameter. In addition, a variety of CCDs as the photodetectors have been developed with reduction of the size and improvement of the precision. As the result, the alignment with the optical axis during the manufacturing process will be more troublesome. In fact, the degree of precision for alignment with the optical axis is measured in about micrometers. More specifically, the tolerance of lens diameter is as small as substantially about tens micrometers. It is hence impractical that the degree of accuracy for alignment with the axis depends on the conventional manner of mounting the optical components to a housing.
For compensation, another technique is disclosed in JP-A 2002-72078 where a marker is provided around the lens by dry etching for use as a reference in the action of alignment with the optical axis. However, the area for such a marker will hardly be spared when the lens is significantly reduced in the overall size.